Unveiling the Correlation Between Structural Stability and Electrochemical Characteristics of Single Crystalline...

Single crystalline (SC) Ni-rich layered lithium metal oxides are promising cathode materials for lithium-ion batteries due to their high theoretical capacity (> 200 mAh g^-1) and reduced cobalt composition. However, electrochemical behavior of Ni-rich materials is underexplored and requires a better understanding to address existing challenges such as elongated Li-ion diffusion pathways and unstable cycling performance. In this study, SC cathode materials with 83% and 90% Ni content are electrochemically cycled at 1 C from 3 to 4.5 V for up to 300 charge/discharge cycles to investigate changes in impedance, non-faradaic and faradaic electrochemical active surface areas, and structural evolution. Non-faradaic electrochemical active surface area (ECSA) measurement increases from 1.81 to 3.30 m² g^-1 for smaller particles sized NCM 90 (3.12 µm) and 3.14 to 3.52 m² g^-1 for larger particles sized NCM 83 (6.18 µm) after 300 cycles. Faradaic ECSA for NCM 83 increased by 34.4% at the reduction stage, whereas NCM 90 reduced by 61.46% contributing to recurring surface reconstruction and microcracking. Micro-computed tomography reveals greater material loss in NCM 83 (≈4.5%) compared to NCM 90 (≈2%), attributed to larger particle size. These insights shed new light on surface and structural changes in SC high-Ni cathodes and their effects on electrochemical performance.